The present invention relates to a light emitting diode (LED) printer, and more particularly to a mechanism for changing the process unit thereof.
In a conventional LED printer as shown in FIG. 1, a control circuit causes an LED head array 4 to expose a photo-sensitive drum 11 to light, in response to printing input data from a computer (not shown). The surface of the photo-sensitive drum 11 is charged with a constant voltage by an electric charger 14, and the portions of the photo-sensitive drum 11 exposed to light by the LED head array 4 come to have reduced voltages, so that an electrostatic latent image is formed on the photo-sensitive drum 11 due to the voltage differences between the initially charged voltage of the portions not exposed to the light and the reduced voltages of the portions exposed to the light. Thereafter, as the photo-sensitive drum 11 is rotated, the toner of a developer 15 is attracted to the surface of the photo-sensitive drum 11 so as to develop the latent image.
Meanwhile, the printing paper is supplied from a paper supplying device 16, aligned by a pair of register rolls 17, and conveyed to a transferring device 18 where the toner developing the latent image on the photo-sensitive drum 11 is transferred to the printing paper. The printing paper adhering to the photosensitive drum 11 by the electrostatic force is separated from the photo-sensitive drum 11 by a separator 19, and conveyed by a conveyor belt 20 to a fixing device 21, where the printing paper is heated and pressed between a heat roll 22 and pressure roll 23 to fix the toner and conveyed to a discharging tray. The residual toner on the photo-sensitive drum 11 is removed by a cleaning device 24, transmitted through an auger 25 to a vessel for collecting the used toner, and the latent image is canceled by the light supplied from a latent image removing lamp 26.
If a printing paper is jammed in the printer, the upper body frame 2 is upwardly pivoted on a hinge 27 detached from the lower body frame 1 to remove the jammed printing paper.
The lower body frame 1 has the paper supplying device 16, fixing device 21, transferring device 18, etc. The upper body frame 2 has a receptacle for receiving the process unit 6 with the cleaning device 24, photo-sensitive drum 11, electric charger 14, and developer 15, and on the upper side thereof is mounted an LED frame 3 for supporting the LED head array 4. The process unit 6 having the cleaning device 24, photo-sensitive drum 11, electric charger 14, and developer 15 is disclosed in U.S. Pat. No. 3,985,436. The LED frame 3 is manually opened and closed pivoting on a hinge 8. Hence, in order to change the process unit 6 first the upper body frame 2 is opened from the lower body frame 1, and then the lever 28 on the frame 3 is pressed so as to release a hook 29 from the holding pin 30 attached to the upper body frame 2. Thus the LED frame 3 is opened upwardly so as to remove the process unit 6 from a unit guide 9.
On the contrary, if the process unit 6 is mounted in the unit guide 9 and the frame 3 including the LED head array 4 is pivoted downwardly on the hinge 8, the hook 29 of the lever 28 is fixedly held by the holding pin 30, so that the LED head array 4 may be positioned facing the photo-sensitive drum 11 through the opening 10 formed in the upper part of the unit guide 9 with a proper interval therebetween.
As stated above such a conventional LED printer is complicated and requires manual disassembling and assembling of related component parts to change the process unit 6.